Not Applicable.
Not Applicable.
The present invention is directed to a stent delivery system which includes a stent retaining sleeve having a ribbed configuration and a perforated portion. The unique characteristics of the present sleeve provides for a delivery system which has superior ability to in immobilize a stent on the catheter surface, and which provides the stent with the stent delivery system with improved safety and ease of use.
The sleeve of the present invention completely covers a stent mounted to a stent delivery catheter. The sleeve has sufficient strength characteristics to securely maintain a stent in its axial position on the delivery catheter, without requiring that the stent first be crimped onto the catheter surface.
It is well understood that stents which are not properly secured or retained to the catheter may slip and either be lost or be deployed in the wrong location or partially deployed. Traditionally, in order to provide proper securement of the stent on the catheter the stent is crimped to a predetermined area of the catheter.
In the past, crimping has been done by hand or by a crimping apparatus, often resulting in the application of undesired uneven forces to the stent. Such a stent must either be discarded or re-crimped. Stents which have been crimped multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. A poorly crimped stent can also damage the underlying balloon.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
The present invention avoids these problems by providing a ribbed retaining sleeve which is capable of securing a stent to the catheter without the need to crimp the stent into place. The ribbed sleeve may be utilized with nearly any type of stent. Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under a contained sheath or sleeve(s) in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter without translocating proximally or distally and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site.
Another invention which may be relevant to the present invention is disclosed in a concurrently filed and commonly assigned U.S. patent application entitled: U.S. Application entitled A NON-CRIMPED STENT DELIVERY SYSTEM, designated by U.S. patent application Ser. No. 09/553,034.
All of the references contained herein, including the co-pending Application listed above, are respectively incorporated in their entirety herein by reference.
This invention provides for an improvement over the prior art, by providing a stent delivery system which includes a self dividing and retracting stent retaining sleeve having a ribbed configuration. The stent may be self-expanding, such as a NITINOL shape memory stent, or it may be expandable by means of an inflatable portion of the catheter, such as a balloon.
The ends of the sleeve overlap the stent and are affixed to the stent delivery catheter. The ends of the sleeve which are affixed to the catheter may be attached thereto in any manner which may be known in the art. For example: the ends may be laser or chemical welded, attached with an adhesive, utilize connection bands, etc. Preferably the sleeve has an interference fit on to the portions of the catheter shaft adjacent to the stent mounting region. The ribbed configuration of the sleeve provides the sleeve with a reduced columnar strength while simultaneously providing radial strength characteristics sufficient to retain and immobilize a non-crimped stent on the catheter surface.
The ribbed configuration of the sleeves provides a plurality of alternating raised and lowered pleats, with the lowered pleats contacting the stent. The sleeve may be composed of an elastic polymer, a non-elastic polymer or any combination thereof.
The reduced columnar strength of the sleeve is at least in part a consequence of having only the downward pleats of the sleeve ribbing, rather than the entire internal surface of the sleeve, frictionally engaging the stent surface. The reduced columnar strength provided by this arrangement allows the sleeve to be readily retracted from the surface of the stent. Preferably, the sleeve has sufficiently low frictional interface with the stent so as to not require the application of a lubricant. Alternatively, the sleeve may be pre-lubricated.
The sleeve includes a perforated portion which splits and divides the sleeve into proximal and distal portions during expansion of the stent. The ribbed configuration of the sleeve further provides a spring or recoil action to the proximal and distal sleeve portions. The recoil action of each sleeve is directed in longitudinally opposing directions and assists in actively retracting the sleeve portions off of the stent in the appropriate direction. When the stent is expanded and the sleeve is split, the recoil action will retract the divided portions of the sleeve toward the respective ends (proximal and distal) of the sleeve which are attached to the catheter. The rupturing of the perforated section of the sleeve, the recoil action and the reduced columnar strength of the sleeve combine to allow the sleeve portions to be pulled completely off of the stent with improved effectiveness.
The ribbed configuration also provides the sleeve with radial strength characteristics sufficient to provide an interference fit between the sleeve and the stent. The interference fit retains the sleeve in a desired position and in a reduced configuration until the recoil action is triggered by the expansion of the stent and the rupture of the sleeve. The radial strength characteristics of the ribbed sleeve portions are such that even during the retraction of the sleeve portions the interference fit is maintained, thus providing a uniform and consistent retraction of the sleeve portions while also ensuring that the retracted sleeve portions remain reduced and thus, do not interfere with the safe removal of the catheter from the vessel subsequent to stent delivery.
The present invention provides for a sheath or sleeve which may completely encompass a stent on the stent delivery catheter, and which may be removed from the stent without the need to employ a retraction wire or member. By providing a sleeve which may cover the entire stent the present invention helps to ensure that the stent is completely immobilized on the catheter surface. In addition, by completely containing a stent within the sleeve the potential for vessel wall damage during the advancement of the catheter is minimized.